Power-Gen Industry – Gas Turbine Failure Risks
Jul 27, 2016
In spite of the rise of renewable energies following government initiatives to reduce reliance on foreign oil imports, thermal power generation still holds a dominant position in the Korean energy market. Over 60% of the electricity provided in Korea is generated in power plants using fossil-fuels such as coal, oil or natural gas. In order to reduce carbon dioxide emissions and pollutants, producers increasingly operate their combined-cycle power plants using natural gas instead of coal.
These power plants usually comprise a few combined-cycle blocks, with three gas turbines and one steam turbine per block. The exhaust gas of each gas turbine is diverted to a heat recovery steam generator (HRSG) controlled by a diverter damper. The most frequent incident that leads to an insurance claim during the operation of this type of combined-cycle power plant is the breakdown of a gas turbine, causing in some cases significant property and business interruption losses.
Gas turbines are usually designed to have four inner row blade rings/vanes, each of them comprising more than 50 blades. In a recent case handled by our team in Korea, our investigation identified that the turbine failure was caused by the detachment of a blade in the first row of turbine blades. As a result, all downstream blades, vanes and other parts of the turbine suffered extensive damage by the impact and debris of the failed blade.
A detailed analysis on the damaged parts of the turbine was conducted by a forensic expert, who couldn’t identify an exact root cause but made various probable conclusions:
- The blade material in question was appropriately manufactured for its application.
- Inevitable fretting wear occurred on mating surfaces of blade root top serration and the disc.
- Fatigue cracking was initiated on the contacting surfaces but wear is not considered as the cause of the failure.
- The measured vibrations at the casings of five gas turbines showed different vibration spectra.
- One of many excitation frequencies detected in the extensive vibration analyses caused by combustion must have been the cause of the blade failure.
The policy in question included Business Interruption (BI) cover. The insured had available the key spare parts necessary to repair the gas turbine except for the turbine casings. After reviewing the situation, we recommended that the insured expedite the repair works, operating 24 hour shifts under the supervision of OEM engineers. The repair works were concluded swiftly and the failed turbine was operational within the 45 days policy waiting period hence there was no BI.
The initial estimated loss, based on the insured’s material damage and BI calculations, was over US$10 million. After prolonged negotiations with the insurers and reinsurers, we suggested the insured purchase all the irreparable parts required for the turbine restoration through competitive bidding to interested OEMs in the gas turbine market thus considerably reducing the material damage loss. The final adjustment was considerably lower than the initial estimate, which was a positive outcome for all parties involved.
